Leveling system for 3D printer

ABSTRACT

A leveling system for a 3D printing system for laser dispensing includes inner and outer frames, each supported at its corners by respective actuators of first and second sets of actuators. The outer frame supports an optical plane within which material to be dispensed by laser irradiation is disposed. The inner frame supports a receiving medium plane within which a substrate on which said material to be dispensed by laser irradiation is disposed. Each actuator operates independently to displace a respective frame corner in the vertical direction. The inner and outer frames each is attached at their respective corners to a respective actuator by a rod, thus allowing the inner and outer frames to freely rotate with respect to one another. An additional frame may support sensors for monitoring the 3D printing system.

RELATED APPLICATIONS

This is a NONPROVISIONAL of U.S. Provisional Application 62/699,085,filed 17 Jul. 2018, incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a system that uses vertical linearactuators at the corners of two frames to ensure parallelism and tocontrol the gap between working planes in a three dimensional (“3D”)printing system for laser dispensing.

BACKGROUND

Within the field of 3D printing there exist a number of drop-on-demand(DOD) printing techniques, some of which involve the fabrication oftwo-dimensional (“2D”) or 3D objects from digital data files undercomputer control. In general, these techniques rely on piezoelectricand/or thermal actuators to eject small amounts (droplets) of liquid(ink) through a nozzle. While these processes may work well for someinks, they tend not to be well-suited for high viscosity inks whichoften clog the small nozzles. Accordingly, methods and apparatus thatemploy lasers to create droplets from donor materials have beendeveloped. These droplets, when solidified in the aggregate, form 2D or3D patterns or structures on receiver mediums.

An example of a laser-based DOD printing apparatus is shown in FIG. 7A.In this approach, a focused laser beam 10 is made incident upon a thinlayer of ink 12 at a small working area 14. The laser heats the ink inthe vicinity of the working area 14, causing a droplet 16 to be jettedtowards a receiver medium 30. The thin layer of ink 12 is transportedlaterally with respect to the stationary laser on an intermediary layer18 (a carrier). The energy absorbed by the intermediate layer partiallyheats the liquid part of the ink and creates a micro-vapor bubble. Thebubble is thermodynamically responsible for the droplet jetting. Atransparent substrate material 20 may be positioned on the side of theintermediary layer opposite the ink layer to ensure the thin layer usedas a transport medium does not bend or break.

FIG. 7B illustrates a more recent jetting arrangement by the presentinventor. Here, a focused laser beam 10 is made incident upon a thinlayer of ink at a small working area. In this arrangement, however, thethin layer of ink is transported into the working area using a mesh-likescreen 22 with small holes or other openings 26 therein arranged in aperiodic fashion. In operation, the laser is focused onto an opening 26(or an area adjacent to an opening) through a transparent substrate 20and the ink within the opening is heated, causing a droplet 24 to bejetted towards a receiver medium 30. Droplet 24 is approximately thesame size as opening 26 and has a volume approximately equal to thevolume of ink contained within the opening 26. The ink, which istypically a highly viscous material (e.g., >50 mPa s) such as a viscousliquid (e.g., a polymer, curable resin, etc.) or nanoparticlesuspension, is coated onto the screen 22 in a uniform layer (with anyexcess being removed prior to exposure to the laser), and is retainedwithin the openings 26 through adhesion to the mesh surfaces and surfacetension. The mesh screen 22 is retained under tension (e.g., lateralstrain with respect to the plane of the screen) 28 as it is transportedthrough the working area by one or more actuators.

Printing with laser dispensing, as in the above-described examples andother arrangements, requires maintaining gaps on the order of no morethan a few hundreds of micrometers between the donor material (e.g.,carrier 18 with ink layer 12 in FIG. 7A or screen 22 in FIG. 7B) and thesubstrate (e.g., receiver medium 30 in FIGS. 7A and 7B). For large sizeobject printing it is difficult to ensure this level of parallelismacross the entire print area.

SUMMARY OF THE INVENTION

In one embodiment of the invention, a leveling system for a 3D printingsystem for laser dispensing includes an outer frame supported at itscorners by respective actuators of a first set of actuators, the outerframe supporting an optical plane within which material to be dispensedby laser irradiation is disposed; and an inner frame supported at itscorners by respective actuators of a second set of actuators, the innerframe being supported by said outer frame and supporting a receivingmedium plane within which a substrate on which said material to bedispensed by laser irradiation is disposed. Each of the actuators of thefirst and second sets is configured to be operated independently, underthe control of a controller, to displace a respective corner of one ofthe inner or outer frames in a direction orthogonal to a reference frameon which the leveling system rests. In one instance, each of the innerand outer frames has three corners, spaced 120° from one another.Additionally, in some cases the inner frame and the outer frame each maybe attached at its corners to a respective actuator by a respective oneof a plurality of rods, thus allowing the inner and outer frames to befree to rotate with respect to one another around axes defined by therods attaching respective corners of the inner and outer frames torespective ones of the actuators. The leveling system may also includean additional frame supported at its corners by respective actuators ofa third set of actuators, where the additional frame supports one ormore sensors for monitoring the 3D printing system.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and notlimitation, in the figures of the accompanying drawings, in which:

FIG. 1 shows an overview of a system for positioning frames of a 3Dprinter in accordance with one embodiment of the invention.

FIG. 2A provides a detailed view of vertical actuators for use in asystem for positioning frames of a 3D printer and configured inaccordance with one embodiment of the invention.

FIG. 2B shows alternatives for actuators that may be used to control thedisplacement of the frames in the vertical direction in accordance withvarious embodiments of the invention.

FIG. 3 illustrates the calculation of precision of angular control inaccordance with one embodiment of the invention.

FIG. 4 is a top view of an axis of rotation in accordance with oneembodiment of the invention.

FIG. 5 shows a side view of rotation of working plane in accordance withone embodiment of the invention.

FIG. 6 shows the actuators operated by a processor-based controller inaccordance with an embodiment of the invention.

FIGS. 7A and 7B illustrate examples of laser-based 3D printingapparatus.

DESCRIPTION OF THE INVENTION

The proposed leveling system provides a plurality of sets of verticallyoriented linear actuators which move the corners of two frames of a 3Dprinting apparatus independently of one another. In one embodiment, twosets of three vertically oriented linear actuators move the corners ofthe two frames. In other embodiments, additional sets or individual onesof actuators may be used at points between the corners of the frames,that is, along the frame members, for example in cases where the frameshave members with articulating joints between the corners, or where thebrittleness, malleability, ductility, or weight of the frame memberswarrants the use of additional actuators along their lengths. One of theframes supports the optical plane of the 3D printing system, which holdsthe material to be printed. The other frame supports the substrate onwhich the material is printed. The system provides accurate control ofthe distance between these two planes in the vertical direction, i.e.,the direction defining the gap between the two planes, and between themand other points in the vertical direction, as well as maintainingparallelism between the two planes.

As is apparent from the illustrations in FIGS. 7A and 7B, 3D printingusing laser dispensing technology involves multiple working planes: anoptical plane on which the laser beam is focused and where the materialfor printing (e.g., ink) is stored, and the receiving medium, which liesin a plane on which the material is deposited during printing. In manysystems there is also a sensor plane in which cameras (or other imagingdevices), and distance and other sensors are positioned. Maintainingparallelism (or other defined relationships) between these variousworking planes and controlling the distance(s) between them presents asignificant challenge to printing at high resolutions. For example,ineffective control over these distances may result in the laser notfocusing properly on the optical plane, printing may be compromised bythe gap between the optical plane and the receiving medium being toosmall or large, or the sensors may move out of their calibratedlocations. The proposed leveling system has the following advantages:

-   -   a. It passively maintains a fixed vertical gap between the        optical plane and the printing plane (i.e., the plane of the        receiving medium).    -   b. The 120° separation between the vertical actuators, as        provided in one embodiment, ensures that lateral forces will not        move the frame out of its x-y position.    -   c. The control of angles of each plane in θ (altitude) and ϕ        (azimuthal) directions in one embodiment is accurate to within        0.006° or less.    -   d. The same actuators control both z (vertical) position and        angle.    -   e. It provides active control of the vertical position of planes        with respect to the laser and with respect to each other.    -   f. It maintains parallelism of the respective planes to ensure        precise printing and accurate sensor readings.    -   g. It leaves a central area of the system open to allow the        laser beam to pass unobstructed.    -   h. Rod end joints allow for free rotation of the frames even if        the actuators are not all moved together.    -   i. It provides reliable, accurate levelling of the working        planes at low cost.

The system consists of two frames used in a laser dispensing (e.g.,Light Initiated Fabrication Technology (“LIFT”)) 3D printer. Referringto FIG. 1, an example of a leveling system 100 in accordance with anembodiment of the present invention is shown. Leveling system 100includes a pair of frames 102, 104 and a plurality of actuators 106,108, in this case three per frame, each positioned at a respectivecorner of one of the frames. A first one of the frames 102 supports theoptical plane, which holds the material to be printed. A second one ofthe frames 104 is supported by the first frame and holds the substrate(receiving medium) on which objects are printed. The first, or outer,frame 102 is acted upon by three actuators 106 located at the corners,spaced 120° from one another, which move the corners in the verticaldirection (that is, in a direction orthogonal to a reference plane onwhich the entire system 100 rests). The second, or inner, frame 104 issimilarly acted upon by another set of three actuators 108. The areainside the outer frame is kept empty to provide space for the laser beam110 to pass and for the print area 112 where the printing takes place.In this example, a laser 114 produces laser beam 110 which is directedto the print area 112 by an optical arrangement (e.g., a scanningmirror) 116, however, in other arrangements a different configurationmay be used.

Each of the actuators of each of the frames may be operatedindependently of the others. Operation of the actuators allows forcontrol of several variables essential to printing. By operating onlythe actuators 108 of the inner frame 104, the gap between the opticalplane and the substrate for printing can be changed. By operating onlythe actuators 106 of the outer frame 102, both the optical and thesubstrate planes can be moved with respect to the laser, or the sensorplane (not pictured). By operating two actuators of any one frame equaldistances in opposite directions, the angle of the center of the frameis changed without affecting its position in the z-direction. Bycombining these movements, complete control of the z-position andangular orientation in the θ (altitude) and ϕ (azimuthal) directions isachieved. This control provides a simple solution for maintainingparallelism of the working planes.

As shown in FIG. 6, operation of any one or more of the actuators oreither or both of the frames is achieved using a processor-basedcontroller 118. Processor-based controller 118 upon or with which themethods of the present invention may be practiced will typically includea processor communicably coupled to a bus or other communicationmechanism for communicating information; a main memory, such as a RAM orother dynamic storage device, coupled to the bus for storing informationand instructions to be executed by the processor and for storingtemporary variables or other intermediate information during executionof instructions to be executed by the processor; and a ROM or otherstatic storage device coupled to the bus for storing static informationand instructions for the processor. A storage device, such as a harddisk or solid-state drive, may also be included and coupled to the busfor storing information and instructions. The subject controller may, insome instances, include a display, coupled to the bus for displayinginformation to a user. In such instances, an input device, includingalphanumeric and/or other keys, may also be coupled to the bus forcommunicating information and command selections to the processor. Othertypes of user input devices, such as cursor control devices may also beincluded and coupled to the bus for communicating direction informationand command selections to the processor and for controlling cursormovement on the display.

The controller 118 may also include a communication interface coupled tothe processor, which provides for two-way, wired and/or wireless datacommunication to/from the controller, for example, via a local areanetwork (LAN). The communication interface sends and receiveselectrical, electromagnetic, or optical signals which carry digital datastreams representing various types of information. For example, thecontroller may be networked with a remote unit (not shown) to providedata communication to a host computer or other equipment operated by auser. The controller can thus exchange messages and data with the remoteunit, including diagnostic information to assist in troubleshootingerrors, if needed.

In operation, the leveling system may be used for positioning the mediaand other components that make up the working planes of the 3D printerfor forming a 3D article by fusion of droplets in forms defined bycross-sections of the object under construction. For example, a firstlayer of individual droplets may be distributed over a receiving mediumwhich is maintained in a plane and position defined by the operation ofactuators 108. This may be accomplished by depositing the droplets,which are produced from a donor medium which is maintained in a planeand position defined by the operation of actuators 106, while moving thereceiving medium within its plane with respect to a nozzle area betweensuccessive droplets to form a relatively thin, approximately uniformlayers of the donor medium (e.g., ink) on the receiving medium and,successively, on previously jetted layers. Once jetted, the dropletscool and solidify in place. Alternatively, entire layers may be printedat a time.

The controller 118 is programmed to cause the laser 114 to emit pulses,thereby creating droplets, at times corresponding to the necessaryapplication of ink for forming the cross-section of the article underfabrication. This may be done, for example, by providing images ofcross-sections, and ensuring that the droplets are jetted when a portionof the receiving medium is positioned, within the plane defined by theoperation of actuators 108, within the print area 112 at a point forwhich material is needed. After each droplet is jetted, controller 118causes the donor medium, the receiver medium, and/or the laser totranslate in preparation for the next application of the laser pulse.For example, the controller may cause the receiving medium to bedisplaced relative to the print area to a next position at which adroplet is to be jetted. The fusion of droplets in locations on thereceiving medium corresponding to the image of the cross-sectional layerof the object to be fabricated form an integral layer of ink having ashape corresponding to that image. In addition, supporting structuresmay be fabricated during production of the object and later removed.Successive layers of droplets are jetted on top of one another tocomplete the object. Alternatively, entire layers may be fabricated at atime, one on top of the other, until the object under fabrication iscomplete. Complex shapes may be fashioned by altering the angulardisplacement of the plane of the receiving medium with respect to theoptical plane, for example through operation of two of the actuators108.

Referring to FIG. 2A, the use of rod ends 120 at the corners of theframes allows the frames to rotate freely about the x and y axes even ifthe three actuators are not moved by the same amount simultaneously. Thepositioning of the actuators at an angle of 120° from one another (perframe) ensures that even if a lateral force acts on the frame, it willnot lose its position in the x- and y-directions. The legs supportingthe actuators are fixed and the angle between the rod 122 and the frameis fixed. Even if a force is applied parallel to one of the rods, so itis free to slide, the other two rods will remain fixed and the x-yposition of the frame will be maintained.

Referring to FIG. 2B, because of its size and construction, the systemcan control the angle of the working planes to a high degree ofprecision in the θ (altitude) and ϕ (azimuthal) directions. In oneembodiment, shown in view (1), linear actuators 124, 126 can move thecorners in the z-direction independently, for example in increments of50 μm or better. Alternatively, the frames may be moved using a leadscrew 128 and nut 130, as shown in view (2). Or, to achieve the desiredlevel of precision, the frames may be moved using piezo translators 132that include a piezo ceramic that expands in a defined direction uponapplication of an electric current (e.g., under the control of thecontroller 118), as shown in view (3). The use of the term “actuator”herein is intended to encompass any or all of these alternative meansfor displacing the frames in the vertical (z) dimension. In the case ofthe piezo translators, the ceramic may be orientated so that when itexpands (at the application of a current under the control of thecontroller), the frame connected to the actuator is displaced along asingle axis (e.g., the z-dimension), along the direction of theexpansion of the crystal. Generally, a number of piezo translators maybe used per actuator and the various piezo translators may be energizedat the same time (or nearly so) so that their actions are coordinatedwith one another. Thus, the piezo translators may be arranged so thatthey impart longitudinal motion to the frame in the same direction andthe translation distance may be proportional to the magnitude of thecurrent applied to the piezo translators. The piezo translator(s)employed in embodiments of the present invention may be any of:longitudinal piezo actuators, in which an electric field in the ceramicis applied parallel to the direction of its polarization; piezoelectricshear actuators, in which the electric field in the ceramic is appliedorthogonally to the direction of its polarization; or tube actuators,which are radially polarized and have electrodes are applied to an outersurfaces of the ceramic so that the field parallel to its polarizationalso runs in a radial direction.

In one embodiment, illustrated in FIG. 3, the actuators 106 of the outerframe 102 are located 1384.68 mm from one another and those 108 of theinner frame 104 are separated by 1064.21 mm. Referring to FIG. 4, whenonly one corner is displaced trough action of an actuator 106 a, theframe will rotate about an imaginary axis 134 that connects the rod endsof the other two corners. If one corner is raised by 50 μm and anotherlowered by 50 the z-position of the center of the frame will not change(see FIG. 5), and the change in angle is given by equations 1 and 2. Thesystem can easily control the angle of the working planes to within0.006°.

$\begin{matrix}{\theta_{1} = {{{arc}\mspace{14mu}\tan\frac{50\mspace{14mu}\mu\; m}{\frac{1}{2} \times 1384.68\mspace{14mu}{mm}}} = {{.0041}{^\circ}}}} & {{Equation}\mspace{14mu} 1} \\{\theta_{2} = {{{arc}\mspace{14mu}\tan\frac{50\mspace{14mu}\mu\; m}{\frac{1}{2} \times 1064.21\mspace{14mu}{mm}}} = {{.0054}{^\circ}}}} & {{Equation}\mspace{14mu} 2}\end{matrix}$

Thus, a system that uses vertical linear actuators at the corners of twoframes to ensure parallelism and to control the gap between workingplanes in a 3D printing system for laser dispensing has been described.

What is claimed is:
 1. A leveling system for a 3D printing system forlaser dispensing, said leveling system comprising: a first framesupported at its corners by respective actuators of a first set ofactuators, said first frame supporting an optical plane within whichmaterial dispensed by laser irradiation is disposed; and a second framesupported at its corners by respective actuators of a second set ofactuators and by said respective actuators of said first set ofactuators so as to passively maintain a fixed gap between said opticalplane and a receiving medium plane and supporting said receiving mediumplane within which a substrate on which said material dispensed by laserirradiation is disposed; wherein each of the actuators of the first andsecond sets is configured to be operated independently under the controlof a controller to displace a respective corner of one of said first orsecond frame in a direction orthogonal to a reference frame on which theleveling system rests and maintain parallelism of the optical andreceiving medium planes.
 2. The leveling system of claim 1, wherein eachof the first frame and the second frame has three corners, spaced 120°from one another.
 3. The leveling system of claim 1, wherein each of thefirst frame and the second frame is attached at its corners to one ofthe respective actuators by a respective one of a plurality of rods,whereby the first and second frames are free to rotate with respect toone another around axes defined by said rods attaching respectivecorners of the first and second frames to respective ones of theactuators.
 4. The leveling system of claim 1, further comprising anadditional frame supported at its corners by respective actuators of athird set of actuators, said additional frame supporting one or moresensors for monitoring said 3D printing system.
 5. A method of orientingcomponents of a 3D printing system for laser dispensing, said methodcomprising: positioning corners of a first frame of a leveling systemusing respective actuators of a first set of actuators, said first framesupporting an optical plane within which material dispensed by laserirradiation is disposed; positioning corners of a second frame of theleveling system using respective actuators of a second set of actuators,said second frame supporting a receiving medium plane within which asubstrate on which said material dispensed by laser irradiation isdisposed; and operating each of the actuators of the first and secondsets of actuators independently of one another by a controller so as todisplace a respective corner of one of said first or second frame in adirection orthogonal to a reference frame on which the leveling systemrests and maintain parallelism of the optical and receiving mediumplanes, wherein during said operating of the actuators, the first frameis supported at its corners by the respective actuators of the first setof actuators and the second frame is supported at its corners by therespective actuators of the second set of actuators and by saidrespective actuators of said first set of actuators so as to passivelymaintain a fixed gap between the optical and receiving medium planes. 6.The method of claim 5, wherein each of the first frame and the secondframe is attached at its corners to one of the respective actuators by arespective one of a plurality of rods, and the method further includesoperating the actuators of the first and second sets of actuators by thecontroller so as to rotate the first and second frames with respect toone another around one or more axes defined by said rods attachingrespective corners of the first and second frames to respective one ofthe first and second sets of actuators.